The present invention relates to the field of telemetry systems. In particular, the invention relates to a method and system for well telemetry.
Coiled tubing is used in conventional well operations to convey downhole tools such as perforating guns, bridge plugs, and packers and to fish for objects downhole. Each of these uses can benefit from accurate measurements made by instruments located at the downhole end of the coiled tubing. For example, a measurement of the depth of a downhole device can be provided in real-time by a Coiled Tubing Collar Locator (CTCL). The CTCL includes an electromagnetic casing collar locator to detect the signal disturbance of the magnetic field as the tool passes a casing collar. This is useful information because the depths of the casing collars are known. In order to communicate that event to the uphole portion of the coiled tubing string, the CTCL changes the pressure of a circulation fluid, such as water, by opening and closing a side port by means of a solenoid valve. After a delay that can be calculated, the change in pressure is measurable uphole indicating the depth of the downhole device. Due to the physical characteristics of the circulation fluid, the maximum rate of data that can be communicated by pressure changes is low. It is difficult, therefore, to transmit more complex measurements, for example, formation measurements, uphole. In addition, some wells do not employ circulation fluid, which disables the CTCL-to-surface communication method.